The present invention relates to a magnetically traceable blasting explosive with stability and a method for the preparation thereof. More particularly, the subject matter of the present invention is a blasting explosive based on a nitrate and nitric ester compound such as ammonium nitrate, nitroglycerin, nitrocellulose and nitroglycol, e.g. dynamite, as well as a chlorate and perchlorate, e.g. ammonium perchlorate, both in the solid and slurried forms, which is magnetically traceable or detectable by virtue of a magnetic powdery material incorporated therein but still has the same degree of stability as the explosive per se without the magnetic material.
Needless to say, explosives of nitrated compounds such as ammonium nitrate, nitroglycerin, nitrocellulose, nitroglycol and the like in the form of, for example, dynamites and explosives of (per)chlorate compounds constitute the main current of the industrial explosives used in mining, civil engineering and the like. One of the very serious problems in the use of industrial explosives, e.g. dynamites, for blasting of soils and rocks is that, when the blasting is performed at several locations with several dynamites in one time, one or more of the dynamites sometimes remain misfired. Such an unexploded dynamite remaining in the field after blasting may be exploded accidentally, when the blasting work is continued with the unexploded dynamites unremoved as embedded in the soil or rock, by the mechanical shock when contacted with a drill tip under working of the excavation or drilling of the soil or rock to prepare for the next blasting. Therefore, it is imperative in the blasting work by use of dynamites or other explosives to quickly and efficiently detect the unexploded ones before continuing the blasting work since otherwise big disastrous damages on manpower are sometimes unavoidable.
The most simple means for detecting such unexploded dynamites is the search with naked eyes although such a method is undesirable not only due to the incomplete detection of the unexploded dynamites but also due to the great labor and danger inevitably accompanying such a work. Accordingly, there have been proposed several methods without the aid of the naked eyes of the workers for the detection of the unexploded dynamites in the field.
Furthermore, another serious problem with respect to an explosive is the detection or search of a malignantly possessed or illegally hidden explosive. For example, explosives stolen and hidden by burglars must be searched by policemen with much labor and time and it is common that passengers are searched before riding an airplane for illegally carried weapons in order to prevent hijacking while the methods used in the airports are powerless to detect non-metallic dangerous articles such as explosives so that development of efficient methods for explosive detection is eagerly desired also in this point.
One of the promising approaches for the safe and efficient detection of an explosive, e.g. dynamite, is the use of a magnetic material. That is to say, each of, for example, dynamites is kept or used as integrally combined with a magnetic material or, in particular, with a magnetic powdery material incorporated thereinto followed by magnetization so as to be easily detected by a magnetic sensor means even in a hidden or covered state. For example, a number of such magnetic explosives are set at the blasting points and, if one or more of the explosives remain misfired after blasting as covered with rocks and sand, the locations of the unexploded explosives can readily be indicated by the magnetic sensor means. A magnetic sensor means installed in an airport can easily point out a hijacker illegally carrying an explosive when the explosive is admixed with a magnetic powdery material and magnetized.
Suitable magnetic materials for such a purpose are of course not limited to any particular types provided that the material is magnetically hard or, in other words, the material has a sufficiently large residual magnetization or coercive force in order to facilitate the detection by a magnetic sensor means. Practically speaking, however, most of the magnetically traceable explosives are impregnated with a magnetic ferrite in a finely pulverized form because of the sufficiently high magnetic performance in addition to the availability with outstanding inexpensiveness in comparison with other types of magnetic materials.
Ferrite magnetics are, however, not quite free from practical problems. One of the serious problems in the use of powders of ferrite magnetics as incorporated in an explosive is that the stability of the explosive is greatly reduced when the explosive compound is in contact with the ferrite powder. In an experiment undertaken by the inventors with dynamites, for example, the time up to the detection of the nitrogen dioxide in the Abel's heat test, which should be compulsorily undertaken as a means for the evaluation of the stability of explosives as specified in the regulation for the Explosive Control Act, was decreased to about one fourth or less when the explosive was admixed with a powdery ferrite in comparison with the same explosive without the ferrite powder. The time will be further shortened when a ferrite-blended explosive is stored over a certain period before its use for blasting. Therefore, the advantages of the magnetic explosives admixed with a ferrite powder is greatly reduced by the increased danger caused by the decomposition during storage against the intention of the use of magnetic explosives.